Analysis and Deterministic Optimization of the Longitudinal Load Distribution Factors of Fine Pitch Gears of the I.S.O. Procedure

Abstract

Estimation of the longitudinal load distribution factors is certainly the most complex, but unfortunately these factors have critical effect on the final rating of gears. The combined lead error of the teeth is usually the most critical accuracy factor in determining the load capacity of fine pitch gear pairs. Since, for similar gears of the same material (i.e, at the same stress level), the longitudinal load distribution factors are found to be higher for fine pitch gears than coarse gears. Many charts, equations and recommendations were stated by many standards and authors in order to estimate these factors. However most of these estimations were based on simple analysis and so many assumptions. For example ISO, method B and other standards such as BS 436 and DIN 3990 assume that the random component of the manufacturing error to be equal to the tolerance on the absolute value of the lead for the least accurate gear. To this must be added the effect of shaft, bearing and case elastic deflections to give the total lead error used to calculate face load distribution factors. In fact, the cumulative effect of combined tolerances on the lead can far exceed this assumption and may produce much greater random alignment variations. In this paper; all possible sources of mesh misalignment are discussed, and an exact formulation is presented for a real single gear box for both overhung and straddle support configuration geometries. In addition, an optimization procedure has been applied to minimize these factors for both cases. The purpose of this paper is to present an alternative generalized approach to the minimization of the face load distribution factors of fine pitch gears after the design stage without altering the design parameters of the gears or their manufacturing process.
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